using System;

using System.Collections.Generic;

using System.Linq;

public class Program

{

    public static void Main()

    {

        var x = "Hello World";

        for(int i = 1; i < x.Length + 1; i++){

            foreach(var z in x.ChunkString(i)) Console.WriteLine(z);

        }

    }

}

​

public static class Ext{

    public static IEnumerable<string> ChunkString(this string val, int chunkSize){

        return val.Select((x,i) => new {Index = i, Value = x})

                  .GroupBy(x => x.Index/chunkSize, x => x.Value)

                  .Select(x => string.Join("",x));

    }

}